1. Field of the Invention
The present invention relates to an optical information processing apparatus in which an optical recording member is scanned in relative manner with a light beam concentrated as a spot for recording and/or, reproducing information.
2. Related Background Art
In the field of optical information processing apparatus mentioned above, there are being developed various apparatus such as the so-called optical disk memory or optical card memory. In the recording, reproduction or erasure of information on the optical recording medium in such apparatus, it is necessary to provide the recording material with optical energy matching the function or property of the material. In general there stands the following relationship between the energies required for recording, reproduction and erasure of a recording medium:
reproducing energy &lt; recording energy&lt; erasing energy
Thus the reproducing energy is selected in the order of 1/5 to 1/20 of the recording energy, in order to prevent erroneous recording in the course of repeated reproductions.
As the energy absorbed by the recording medium is related to the power of the irradiating light energy and the irradiating time, it is governed not only by the intensity of the reproducing energy, but also by the moving speed relative to the recording medium, or the speed of the recording medium crossing the irradiating light. Consequently, even with a reproducing light of a very low energy level, if the moving speed of the recording medium is below a predetermined value, the irradiated area absorbs a level of energy exceeding the level required for recording, thus causing erroneous recording or eventual destruction of the recording medium. Such trouble may also occur at information recording. Even during the irradiation with a light beam of an ordinary recording intensity, if the relative speed of the light beam and the recording medium is lowered, the irradiated area may absorb a level of energy exceeding the recording level, thus eventually causing destruction of the recording material.
In order to prevent such trouble, the Japanese Patent Laid-open No. 67303/1977 discloses an optical information processing apparatus equipped with a mechanism for detecting the relative speed of the light beam and the recording medium, and, if that speed is below a predetermined value, inserting a shutter or a filter between the light source and the recording medium, thereby interrupting the light beam or reducing the intensity of the light beam.
However such apparatus is associated with the drawbacks of an increased number of component parts or of an increased dimension, because of the presence of the shutter and related mechanisms.
Also, the U.S. patent application Ser. No. 812,995 (allowed) of the assignee of the present application (Filed Dec. 24, 1985), proposes an optical information processing apparatus capable of preventing the above-mentioned trouble by
(i) turning off the light source; PA0 (ii) reducing the intensity of the light source; or PA0 (iii) displacing the light beam to another location; after the lapse of a predetermined time when the relative speed of the light beam and the recording medium becomes lower than a predetermined value. However the method (i) requires a certain time before the light emission from the light source is stabilized at the re-start of the reproducting operation etc. Also the method (ii) may not be able to provide a desired intensity, as the intensity after reduction is subjected to certain limitation. For example the semiconductor laser can change the light intensity only within a certain range, since the laser oscillation cannot be induced with a current not reaching the threshold value. In addition, the method (ii) is associated with the drawback of necessary waiting time for stabilization of the output when the intensity is elevated again, as in the method (i). On the other hand, the method (iii) is effective for preventing erroneous recording in the stand-by state, but is unable to cope with a malfunction of the scanning means for the light beam.